When the activity of a catalyst (amount of olefin polymer obtained per unit catalyst) used for the olefin polymerization to produce the olefin polymer is sufficiently high, there is no need to remove a catalyst residue from the polymer obtained after the polymerization, and therefore the production process of the polymer can be simplified. Thus, such a catalyst can be said to be extremely high in an industrial utility value.
In the production of the olefin polymer, it is desired that adhesion of the polymer to a polymerization vessel is as little as possible, because the adhesion causes various problems in operation to result in deterioration of an operation efficiency.
With respect to powder properties of the olefin polymer obtained, it is desired from a viewpoint of an operational stability and efficiency that the bulk density thereof is high, its particle size distribution is narrow, and its flowability is superior.
Further, it is desired that the content of lower molecular weight components in the olefin polymer obtained is as low as possible, because the lower molecular weight components affect the transparency, impact resistance and blocking property of a film prepared from the olefin polymer.
In the field of solid catalysts for olefin polymerization, polymerization activity has been markedly improved by using a solid catalyst component obtained by a combination use of a specific magnesium compound and a specific titanium compound, as disclosed in, for example, JP-B-46-34092, JP-B-47-41676, JP-B-55-23561 and JP-B-57-24361.
In the polymerization of propylene, it is known that a polymer of high crystallinity can be produced with a high activity by using an oxygen-containing electron donor, such as esters, as an internal donor of a solid catalyst component, as disclosed in, for example, JP-B-52-39431, JP-B-52-36786, JP-B-01-28049 and JP-B-03-43283.
However, the olefin polymer obtained by using the former catalyst system disclosed in, for example, JP-B-46-34092, is not satisfactory in its powder properties and blocking property, and also when the latter catalyst system disclosed in, for example, JP-B-52-39431, is used for copolymerization of ethylene with another α-olefin, the resulting olefin copolymer is not satisfactory in its powder properties and blocking property.
Each of the references referred to herein is incorporated by reference in its entirety.